Motion picture photography and projection is commonly accomplished via a series of still photographs on a strip of sprocketed celluloid film. In the camera, conventions of the motion picture industry call for a standardized frame rate of 24 frames per second, most commonly photographed using a rotating shutter in the camera such that during 360 degrees of shutter rotation, half of the time (1/48th of a second) the shutter is open while the film is held fixed in the camera aperture, and the other half of the time the shutter is closed in order for a mechanical movement to transport the film to the next frame, utilizing the perforations on the film to register to either sprockets or claws to move the film as well as hold it in position during each exposure.
For projection, the same frame rate of 24 is used, however the shutter speed is doubled, so that each frame of film is shown twice before proceeding to the next frame. The shutter is often called a “butterfly”, having two openings of 90 degrees each, and two closures of 90 degrees each, thus still rotating at 360 degrees per frame. During one of the shutter closures the film is advanced to the next frame using a mechanical Geneva mechanism, or sometimes a low inertia electric stepper motor. The reason for the double shuttering, which creates a 48 cycle-per-second rate, is to reduce objectionable perceived flicker of the image on the screen, which is limited in brightness to not more than 16 foot lamberts. Projection brighter than 16 foot lamberts reintroduces objectionable perceived flicker.
An objectionable artifact of this double-shuttering of each image frame is a substantial loss of motion continuity due to the fact that the image does not contain new motion position on each flash, resulting in a stroboscopic effect retained in the human retina. This loss of motion continuity is exacerbated in stereoscopic motion pictures, since frame-to-frame image displacement is often equal to, or more than, the left eye-right eye image separation needed for stereoscopic imagery.
With the advent of digital photography and digital projection, however, it is now possible to consider an alternative methodology of photographing and projecting a series of images in such a manner as to fully retain both temporal motion continuity, while also diminishing the objectionable artifacts of the 24 fps world standard.
It is common knowledge amongst cinematographers, directors, and editors that frame-to-frame object or image motion must be substantially limited in order to avoid objectionable blurring or strobing. Blurring results from object/image motion that occurs during the shutter opening of 1/48th of a second. Strobing occurs when the image displacement from one frame to the next becomes so great that the eye cannot integrate the sequence of frames into a smooth motion. Screen size is considered a limitation, since frame-to-frame image displacement can become quite objectionable on large screens due to angular displacement of frames on fast action. IMAX is a good example of this phenomenon, and IMAX films routinely slow their camera and object motion in order to avoid objectionable blurring and strobing.
Another shortcoming of the 24 frame standard is that when projecting a 3D movie, which includes two simultaneous projections of left and right eye imagery, if the motion displacement or blur between frames exceeds the displacement between right and left eye convergence angles, the 3D effect is lost and is overcome by blurring and strobing of the image.
An earlier invention and patent for the Showscan system disclosed the photographing and projecting of motion pictures at sixty frames per second. See U.S. Pat. No. 4,477,160, incorporated herein by reference in its entirety. The Showscan system resulted in a solution for the above shortcomings of conventional film, while demonstrably increasing a sense of “liveness” and audience stimulation. Each frame was shown only once, thus not using a double-bladed shutter, and at a shutter opening of 120th of a second, blurring of the recorded image was substantially reduced. At a projection rate of 60 frames per second, there was no apparent flicker at any increased screen brightness, and there was no discontinuity of motion. 3D films photographed and projected in Showscan had no objectionable object/image motion limitations that would adversely affect the 3D illusion.
Nevertheless, worldwide motion picture audiences are accustomed to the 24 frames per second standard, although the advent of 3D production and exhibition is revealing the shortcomings of the 24 fps standard, and since the film is attempting to create a more “immersive” experience for the viewer, it is now possible to consider a high frame rate solution that solves problems in both photography and projection. Accordingly, embodiments of the present disclosure are intended to take advantage of emerging digital technologies of electronic cinematography and digital projection, which no longer requires adherence to the world standard of 24 fps. In fact, the entire idea of “frames” as individual still photographs projected in rapid succession can now be revised to a new concept of overall fluid image flow by substantially increasing the number of frames per second. Since the photographed standard 24 fps film must be projected at a higher flash rate in order to avoid perceived flicker, and also solve the requirements for polarized stereoscopic projection, it is common to interleave alternating left and right eye frames via several alternating flashes.
For example, the RealD digital polarization technique alternately polarizes left and right eye images by sequentially flashing each frame as much as three times, resulting in a “flash rate” of 144 flashes (each frame being “shown” onto the screen three times). In this way a 24 fps film can be projected by a single digital projector. Since a new objective of “immersive stereoscopic imagery” is emerging, it is now possible to consider that each of the 144 flashes could actually be new frames of motion information, photographed at 144 frames per second. One of the major shortcomings of the present standards used when projecting 24 fps stereoscopic films is that the temporal information rate is unable to satisfy the need to reduce or eliminate blurring and strobing of the image that is quite objectionable when viewing the film stereoscopically. The advent of this invention is that by alternately photographing 72 left eye images interleaved with 72 right eye images, there remains perfect temporal continuity of the imagery.
In fact, filmmakers often desire to include in their films as much action as possible in order to instill a sense of participation and excitement in viewers, resulting in a sense of sensory immersion. Yet, a tremendous amount of this action is lost in blur if the frame rate is limited to 24 fps. And in 3D, at 24 fps the image may lose all sense of stereoscopic dimension due to both blur and strobing.
In view of the above, there is a need for a digital cinematographic and projection process that provides 3D stereoscopic imagery that is not adversely affected by the standard frame rate of 24 frames per second, as is the convention in the motion picture industry worldwide.